1. Field of the Invention
The present invention relates generally to bone anchored implant devices, and more particularly, to a percutaneous implant abutment for bone anchored implant devices adapted to be anchored in the craniofacial region of a person.
2. Related Art
There are a variety of medical devices that include a bone anchored implant device. An example of such medical devices is the, bone conduction hearing aid devices such as bone anchored hearing implants. An example of a bone anchored hearing implant is the Baha®, commercially available from Cochlear Bone Anchored Solutions AB in Gδteborg, Sweden. The Baha® and other bone anchored implant devices comprise an external unit which transforms sound to mechanical vibrations which are conducted via the abutment and the fixture into the bone of the skull. The vibrations are transmitted mechanically via the skull bone directly to the inner ear of a person with impaired hearing and allows for the hearing organ to register the sound. A hearing aid device of the BAHA® type is connected to an anchoring element in the form of an implanted titanium screw installed in the bone behind the external ear. Sound is transmitted via the skull bone to the cochlea irrespective of a disease in the middle ear. The bone anchoring principle means that the skin is penetrated which makes the vibratory transmission very efficient.
This type of hearing aid device has been a revolution for the rehabilitation of patients with certain types of impaired hearing, but also as anti-stuttering means. It is very convenient for the patient and almost invisible with normal hair styles. It can easily be connected to the implanted titanium fixture by means of a bayonet coupling or a snap in coupling. One example of this type of hearing aid device is described in U.S. Pat. No. 4,498,461 and in SE 9702164-6 it is described a one-piece implant of this type, in which the fixture is integrated with a first coupling device. In WO 2005/037153 it is described how this type of hearing aid device can be used as an anti-stutte-ring device.
A well known problem with percutaneous implants is the infections and inflammation at the skin-implant interface. The infections are a result of bacterial colonization occurring at the area around the interface. There is generally a lack of integration of the skin to the implant which results in a gap between the two. This gap is unfortunately an ideal environment for the bacteria and if this zone is not properly managed, it is likely that an infection will occur. By creating an integration of the skin to the implant the adverse skin reactions associated with bone anchored percutaneous implants are expected to be reduced.
Creating integration between the skin and the implant requires that the implant is suitable for this purpose and that the soft tissue does not dissociate itself from the skin penetrating implant abutment by encapsulating the abutment in fibrous tissue.
In the field of dental implants it is previously known to use different types of abutments which penetrate the oral mucosa. However, it should be understood that there is a physiological difference between breaching the skin barrier compared to the oral mucosa. In the oral cavity the skin is not involved and there is another type of force situation. In contrast to dental implants the present invention relates to extraoral implants.
It is recognized that bone anchored percutaneously implants are subjected to mostly shear forces, while percutaneously implants which are not bone anchored are subjected to several other types of forces, such as pull and torsion. Such different types of forces are also mostly involved in dental applications. Mostly shear forces are especially the case for implants with inherent movements such as bone anchored hearing implants due to the generation of vibratory movements.
It is also recognized that the effect that the shear forces has on the skin leads to tissue damage not only from a mechanical point of view but, more importantly, an indirect biological reaction which leads to foreign body reaction or dissociation from the material (encapsulation of the implant by fibrous tissue, etc). Some reactions are acute and some are noticed after several weeks.